Buggy code:
public void fillRectangle ( Rectangle rect ) { } public void fillRoundRectangle ( int x , int y , int width , int height , int arcWidth , int arcHeight ) { } void flush ( ) { } public int getAdvanceWidth ( char ch ) { } public Color getBackground ( ) { } public Pattern getBackgroundPattern ( ) { } public boolean getAdvanced ( ) { } public int getAlpha ( ) { } public int getAntialias ( ) { } public int getCharWidth ( char ch ) { } public Rectangle getClipping ( ) { } public void getClipping ( Region region ) { } public int getFillRule ( ) { } public Font getFont ( ) { } public FontMetrics getFontMetrics ( ) { } public Color getForeground ( ) { } public Pattern getForegroundPattern ( ) { } public GCData getGCData ( ) { } public int getInterpolation ( ) { } public LineAttributes getLineAttributes ( ) { } public int getLineCap ( ) { } public int [ ] getLineDash ( ) { } public int getLineJoin ( ) { } public int getLineStyle ( ) { } public int getLineWidth ( ) { } public int getStyle ( ) { } public int getTextAntialias ( ) { } public void getTransform ( Transform transform ) { } public boolean getXORMode ( ) { } public int hashCode ( ) { } void init ( Drawable drawable , GCData data , int context ) { } public boolean isClipped ( ) { } public boolean isDisposed ( ) { } boolean isIdentity ( float [ ] transform ) { } public void setAdvanced ( boolean advanced ) { } public void setAlpha ( int alpha ) { } public void setAntialias ( int antialias ) { } public void setBackground ( Color color ) { } public void setBackgroundPattern ( Pattern pattern ) { } void setClipping ( int clipRgn ) { } public void setClipping ( int x , int y , int width , int height ) { } public void setClipping ( Path path ) { } public void setClipping ( Rectangle rect ) { } public void setClipping ( Region region ) { } void setCGClipping ( ) { } void setCGFont ( ) { } public void setFillRule ( int rule ) { } public void setFont ( Font font ) { } public void setForeground ( Color color ) { } public void setForegroundPattern ( Pattern pattern ) { } public void setInterpolation ( int interpolation ) { } public void setLineAttributes ( LineAttributes attributes ) { if ( ( handle ) == 0 ) SWT . error ( ERROR_GRAPHIC_DISPOSED ) ; if ( attributes == null ) SWT . error ( ERROR_NULL_ARGUMENT ) ; int mask = 0 ; float lineWidth = attributes . width ; if ( lineWidth != ( data . lineWidth ) ) { mask |= ( GC . LINE_WIDTH ) | ( GC . DRAW_OFFSET ) ; } int lineStyle = attributes . style ; if ( lineStyle != ( data . lineStyle ) ) { mask |= GC . LINE_STYLE ; switch ( lineStyle ) { case SWT . LINE_SOLID : case SWT . LINE_DASH : case SWT . LINE_DOT : case SWT . LINE_DASHDOT : case SWT . LINE_DASHDOTDOT : break ; case SWT . LINE_CUSTOM : if ( ( attributes . dash ) == null ) lineStyle = SWT . LINE_SOLID ; break ; default : SWT . error ( ERROR_INVALID_ARGUMENT ) ; } } int join = attributes . join ; if ( join != ( data . lineJoin ) ) { mask |= GC . LINE_JOIN ; switch ( join ) { case SWT . CAP_ROUND : case SWT . CAP_FLAT : case SWT . CAP_SQUARE : break ; default : SWT . error ( ERROR_INVALID_ARGUMENT ) ; } } <START_BUG> int cap = attributes . join ; <END_BUG> if ( cap != ( data . lineCap ) ) { mask |= GC . LINE_CAP ; switch ( cap ) { case SWT . JOIN_MITER : case SWT . JOIN_ROUND : case SWT . JOIN_BEVEL : break ; default : SWT . error ( ERROR_INVALID_ARGUMENT ) ; } } float [ ] dashes = attributes . dash ; float [ ] lineDashes = data . lineDashes ; if ( ( dashes != null ) && ( ( dashes . length ) > 0 ) ) { boolean changed = ( lineDashes == null ) || ( ( lineDashes . length ) != ( dashes . length ) ) ; for ( int i = 0 ; i < ( dashes . length ) ; i ++ ) { float dash = dashes [ i ] ; if ( dash <= 0 ) SWT . error ( ERROR_INVALID_ARGUMENT ) ; if ( ( ! changed ) && ( ( lineDashes [ i ] ) != dash ) ) changed = true ; } if ( changed ) { float [ ] newDashes = new float [ dashes . length ] ; System . arraycopy ( dashes , 0 , newDashes , 0 , dashes . length ) ; dashes = newDashes ; mask |= GC . LINE_STYLE ; } else { dashes = lineDashes ; } } else { if ( ( lineDashes != null ) && ( ( lineDashes . length ) > 0 ) ) { mask |= GC . LINE_STYLE ; } else { dashes = lineDashes ; } } float dashOffset = attributes . dashOffset ; if ( dashOffset != ( data . lineDashesOffset ) ) { mask |= GC . LINE_STYLE ; } float miterLimit = attributes . miterLimit ; if ( miterLimit != ( data . lineMiterLimit ) ) { mask |= GC . LINE_MITERLIMIT ; } if ( mask == 0 ) return ; data . lineWidth = lineWidth ; data . lineStyle = lineStyle ;

Fix:
int cap = attributes . cap ;